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Results for “refractive error”

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PubMed1983

An evaluation of the Cavitron Autorefractor 7 with contact lenses and non contact lens wearing patients.

The Autorefractor 7 is a microcomputor assisted electro-mechanical optical system recently introduced to the professions for the subjective measurement of refractive error, phorias, and accommodative capacity. In this study of 450 eyes, 150 were wearing hard contact lenses, 150 wearing soft lenses, and 150 habitually wore a spectacle correction. Comparisons involved only the subjective refractive feature of the instrument and indicated no predictable difference in the three groups. Comparison of the Autorefractor 7 and clinical subjective refraction with the phoropter, however, showed that the instrument is reliable in the majority of cases but has a tendency to overcorrect myopia and astigmatism.

Accommodation, Ocular↗
PubMed1992

Nonulcerative complications of contact lens wear. Relative risks for different lens types.

A case-control study was used to evaluate the relative risk (RR) of acute contact lens-related disorders. The study sample comprised new patients wearing contact lens presenting at the accident and emergency department at Moorfields Eye Hospital, London, England, in 12 months. Disorders were classified by pathogenesis. Compared with gas-permeable hard contact lenses (the referent), extended-wear soft contact lenses were related to the largest overall RR for any complication (2.7 [95% confidence limits, 1.73, 4.16]), whereas for daily wear soft contact lenses the overall RR was 1.3 (confidence limits, 1.0, 1.72). Relative risks were greatest for extended-wear soft contact lens wearers with metabolic disorders (2.1 [confidence limits, 1.28, 3.4]) and for such wearers with sterile infiltrates (2.4 [confidence limits, 1.22, 4.84]). Among those using daily wear contact lenses, RR was highest for those with toxic/hypersensitivity disorders (5.9 [95% confidence limits, 3.27, 10.49]). Severe complications involving greater morbidity occurred more frequently with extended-wear soft contact lenses. This could be reduced by selecting a more appropriate lens type to correct low refractive errors.

Acute Disease↗
PubMed1999

Contact lens management of patients who have had unsuccessful refractive surgery.

The advent of corneal refractive surgery has, inevitably, resulted in the occasional need for contact lens fitting after surgery. For each new, developing procedure, new contact lens fitting challenges arise. The literature on contact lens use after radial keratotomy is rich and well known, but reports on the use of contact lenses after photorefractive keratectomy or laser-assisted in situ keratomileusis are few and far between. This review summarizes the prevailing clinical opinions on the contact lenses and contact lens fitting methods that are most effective after refractive surgery that results in high refractive error, irregular astigmatism, or anisometropia.

Anisometropia↗
PubMed1979

A first year's experience with intraocular lens implantation.

A microsurgical modification of Binkhorst's "open sky" technique of extracapsular cataract extraction was developed for intraocular lens implantation. Clear visualization of both anterior and posterior capsule is stressed and risky aspiration is minimized. Thirteen cases operated upon in the first year are described. Synechiae to the haptics occurred when mydriasis was not prompt. All but one obtained useful naked acuity. Binocularity depended chiefly upon the acuity of the opposite eye. Pre-calculation of lens power reduced the spread of postoperative refractive errors although deviation was greater than expected and myopia overaccentuated. High astigmatic errors occurred in three patients.

Aged↗
PubMed1991

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. The Perk Study Group.

In the Prospective Evaluation of Radial Keratotomy (PERK) Study, 793 eyes of 435 patients with 2 to 8 diopters (D) of myopia received a standardized surgery consisting of 8 incisions with a diamond-bladed knife set at 100% of the thinnest paracentral ultrasonic corneal thickness measurement and a diameter of the clear zone of 3.0 to 4.5 mm; 97 eyes (12%) received an additional 8 incisions. There were 757 eyes (95%) followed for 3 to 6.3 years. After surgery, uncorrected visual acuity was 20/40 or better in 88% of eyes. The refractive error was within 1 D of emmetropia for 64% of eyes; 19% were myopic and 17% were hyperopic by more than 1 D. Between 6 months and 5 years after surgery, 22% of the eyes had a refractive change of 1 D or more in the hyperopic direction. For 25 eyes (3%) there was a loss of 2 or more lines of best spectacle-corrected visual acuity.

Adult↗
PubMed2002

Predicting the refractive outcome after cataract surgery: the comparison of different IOLs and SRK-II v SRK-T.

AIM: To determine any differences between the predictive abilities of the IOL calculation formulas of SRK-II and SRK-T and to compare these using two different IOL types. METHODS: A prospective, consecutive, single surgeon clinical trial was conducted on 400 consecutive patients who received routine, standardised phacoemulsification cataract surgery. 200 had cataract surgery and had the Alcon MZ30BD, a 5.5 mm one piece PMMA IOL, and another 200 cases used the Chiron C11UB, a silicone plate haptic IOL. The data used optimised A-constants. The measures were preoperative axial length and keratometry, IOL implanted, and refractive error at 4-6 weeks postoperatively. RESULTS: There was no significant difference between the predictive abilities of SRK-II or SRK-T. For the Alcon and Chiron lens respectively, prediction errors using SRK-II were <0.5 dioptres in 58% and 70% and for <1.0 dioptres in 84% and 92%. These differences were statistically significant (chi(2), p=0.02). CONCLUSION: There are differences in the predictability of refractive outcomes between intraocular lens styles.

Biometry↗
PubMed1981

The ratio of the size of the optic cup (as determined by the place where the vessels deviate) to size of the disc.

The vessel deviation to disc ratio (VDR) of the optic nerve head can be defined for a given meridian as the ratio of the size of the cup as indicated by small blood vessel deviation in that meridian to the size of the disc. Thus, VDR is a relative measure similar to cup/disc ratio. The difference between VDR and other methods of measuring cup/disc ratio is that the former identifies the rim of the cup with the deviation or bending of the small blood vessels as they fan out over the disc, whereas the latter determine the location by the other criteria which vary from examiner to examiner. The purpose of this study is to quantify the variation in VDR and its relation to age, refractive error, and sex.

Adolescent↗
PubMed1987

Significance of intraocular lens power calculation.

A total of 94 patients underwent extracapsular cataract extraction and insertion of Sinsky style two-loop posterior chamber intraocular lenses. Forty-six eyes received a standard power IOL and 48 eyes were given a preoperatively calculated IOL. A significant difference was found in the two groups with regard to the postoperative refractive error and uncorrected visual acuity.

Adult↗
PubMedDate not supplied

Near retinoscopy in accommodative esotropia.

We tested whether near retinoscopy, a noncycloplegic retinoscopic technique, was applicable to the optic correction of patients with accommodative esodeviations. We performed a study in 17 patients with accommodative esotropia to compare the refractive values obtained by near retinoscopy and by cycloplegia, as measured by two examiners. The interobserver variability was the same for the two techniques for the refractive values of the horizontal and vertical meridia and spherical equivalent. For the astigmatism, there was greater variability for near retinoscopy. The correlation between the two methods was good, but the variability of the differences was high. We recommend that near retinoscopy should be employed only as a noninvasive method for screening refractive errors in children.

Accommodation, Ocular↗
PubMed1975

Vision in the water without a facemask.

Distance and size estimates and stereoacuity judgments were made in water by divers, both with and without facemasks. Without the mask, only stereoacuity was markedly degraded. Distance estimates were slightly more accurate, despite a great decrease in the range of visibility. Size estimates were slightly too small. Divers with refractive errors did not appear to be more handicapped than those with normal vision.

Distance Perception↗
PubMed2004

Test-retest reliability of clinical Shack-Hartmann measurements.

PURPOSE: To evaluate the stability of clinical monochromatic aberrometry measurements over a wide range of time scales. METHODS: Monochromatic aberrations in four normal eyes were measured with a clinical Shack-Hartmann aberrometer. A chin rest or a supplemental bite bar attachment was used to stabilize head and eye position. Five repeated measurements were taken within one test (5 frames, t < 1 second) without realignment. With realignment between each measurement, aberration measurements were repeated five times (t < 1 hour) on each day, at the same time of day on five consecutive days, and again on 5 days at monthly intervals. A control experiment studied the effect of systematically misaligning the eye to determine whether fixation errors can account for the variation in the repeated measurements. RESULTS: Variability of wavefront root mean square (RMS) error (excluding defocus and astigmatism) was tracked across repeated measurements. Variances for different time scales were: 8.10 x 10(-5) microm2 (t < 1 second), 3.24 x 10(-4) microm2 (t < 1 hour), 4.41 x 10(-4) microm2 (t < 1 week), 9.73 x 10(-4) microm2 (t < 1 year). Bite bar and chin rest data were almost identical. Rotational fixation error up to 3 degrees accounts for only part of the variability. CONCLUSIONS: Increased variability in aberration maps between days and months indicates biological fluctuations that are large enough to prevent achievement of "perfect vision," even in the unlikely event that spherical and astigmatic refractive errors are corrected perfectly. However, lack of stability does not justify withholding treatment. A lasting benefit of aberration correction is expected despite temporal variability.

Adolescent↗
PubMed1979

Prevalence of monocular amblyopia among anisometropes.

Some 167 subjects showing anisometropia of at least 2 D, were selected from the records of the eye clinic of the Ramathibodi hospital in Bangkok, Thailand and 472 subjects showing anisometropia of at least 1 D were selected from the clinic records of the Indiana University, School of Optometry. The incidence of amblyopia (20/30 or less) was found to be 100% among least meridional hyperopic anisometropes of 3.5 D and greater, and among myopic anisometropes of 6.5 D and greater. Lower levels of anisometropia showed a smaller proportion of amblyopia. Comparable results were obtained for anisometropes computed in terms of mean spherical refractive error. Significant difference was not apparent for the Thai and American groups.

Adolescent↗
PubMed1988

Ocular effects of hard gas-permeable-lens extended wear.

Thirty-five myopic subjects were fitted with rigid gas-permeable lenses for 6 months of extended wear (EW). These lenses had an average oxygen transmissibility of 37 x 10(-9) (cm x ml x O2)/(s x ml x mm Hg). For six monthly morning visits subjects reported with one eye patched; corneal thickness, corneal curvature, refractive error, endothelial photomicroscopy, and slitlamp examinations were done on both eyes. The average morning corneal swelling was 5.9 +/- 3.3%. Corneal curvature showed 0.24 +/- 0.44 D flattening in the steep meridian and 0.20 D steepening in the flat meridian. Spectacle refraction and corrected visual acuity changes were small in the spherical and cylindrical components. Complications that were important clinically included 10% lens adherence syndrome, 20% superficial limbal keratitis, 6.5% epithelial microcysts, and some increase in endothelial polymegathism. No infections, red eye responses, or infiltrative keratitis were observed during the 6-month follow-up period. These results suggest that hard-lens EW is feasible and that lenses with this Dk/L value will meet oxygen requirements for many patients; however, some patients will require lenses of higher oxygen transmissibility to avoid undesirable complications.

Cell Count↗
PubMed1979

A new optical modality to overcome diplopia.

The author has presented a new method to correct vertical diplopia using a prism contact lens. To the present time, its application has been limited to contact lenses correcting refractive errors of less than 3D and to ground-in prisms of not more than 6 delta. The field is new. Technical, mathematical, and clinical advances should eventually allow the use of stronger prisms over a wider range of refractive corrections.

Contact Lenses↗
PubMed1984

Noncycloplegic vs cycloplegic retinoscopy in pre-school children.

Refractive errors in 311 children between the ages of 18 and 48 months were assessed utilizing standard cycloplegic retinoscopy and a noncycloplegic near retinoscopy technique as promulgated by Mohindra. Results from this study indicate little agreement between the two objective refraction methods.

Child, Preschool↗
PubMed2002

[Full optical correction after cycloplegia in headache].

PURPOSE: To study the advantages of cycloplegia in the accurate assessment of refractive errors and to evaluate the impact of full optical correction in the course of headache. MATERIAL: and methods: A prospective study was carried out in 164 eyes of 82 patients with headache. Corrected visual acuity was 10/10 in all cases. Refraction was measured before and under cycloplegia by cyclopentolate with a CANON R 50 infrared autorefractometer. Full optical cycloplegic correction based on the value of refraction under cycloplegia was prescribed in all cases. Mean follow-up was 10 months. Statistical analyses were used: Student's t test, Pearson coefficient correlation, and Chi2. RESULTS: Under cycloplegia, hypermetropia was significantly the most frequent ametropia (67.1%, p<10(- 9)). The difference between the spherical equivalent, before and during cycloplegia, was highly significant (p<10(- 5)) at 0.79. Optical correction eliminated headaches in 76.5% of the cases. CONCLUSION: The authors conclude on the role of accommodation in headache onset and the need to continue cycloplegia until the age of 45. The importance of optical correction in alleviating headaches is underlined.

Accommodation, Ocular↗
PubMed1984

Optometric findings in children with cerebral palsy.

Optometric examinations of 73 children with normal intelligence but with cerebral palsy revealed a higher than normal incidence of strabismus, significant refractive errors, amblyopia, nystagmus, and optic atrophy.

Accommodation, Ocular↗
PubMed1984

Effect of target configuration on the measurement of astigmatism.

In this study, five dissimilar crossed cylinder targets were used to determine the cylindrical component of the refractive error of 30 subjects. Our purpose is to see if variations in target configuration affect the results of the test. Although there are statistical differences when targets with different configurations are used in determining astigmatism subjectively, these differences are not clinically significant if we assume that the least amount of error required for clinical significance is +/- 0.25 D. We conclude that dissimilar crossed cylinder targets yield similar astigmatic findings clinically.

Adult↗